The present invention relates generally to communications systems, and more particularly, to outage detection in a time division multiplex communications systems.
In this communication age, content providers are increasingly investigating ways in which to provide more content to users as well as interfacing with users.
Communication satellites have become commonplace for use in many types of communication services, e.g., data transfer, voice communications, television spot beam coverage, and other data transfer applications. As such, satellites transmit and receive large amounts of signals used in either a xe2x80x9cbent pipexe2x80x9d or xe2x80x9cspot arrayxe2x80x9d configuration to transmit signals to desired geographic locations on the earth.
Because the frequency of resources is scarce for over-the-air transmission, various encoding schemes are used to provide a greater number of communication signals within an allocated communication band. Such encoding schemes include code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), or combination of these schemes. Further, to prevent interference the schemes may operate at various frequencies.
In TDMA mobile transmission systems, occasional channel impairments are inevitable. This may occur due to a link outage due to a full obstruction of the radio path. Blockage of the radio path may result in a receive signal being weak or extremely noisy. Commonly, when an outage occurs no-target tracking or drifting of synchronization systems occurs.
Outage detection is conventionally based on observation of the signal-to-noise ratio (SNR) or a cyclic redundancy check (CRC). The application of SNR is constrained by its limited confidence range. That is, reliable detection may not be achieved when the channel condition is unfavorable. In its implementation, a CRC is usually performed on different hardware from that of the demodulation hardware. Thus, such systems require complicated logic signaling interactions. For both SNR and CRC based systems, the detection is performed after the demodulation. Because of this, the computation is lengthy.
It would therefore be desirable to design an simple outage detection procedure with less computation that also allows quick resumption of transmission and reliable maintenance of synchronization after an outage occurrence.
It is therefore one object of the invention to provide an improved outage detection system in a TDMA system.
In one aspect of the invention, a method for operating a communication system comprises the steps of:
receiving a received signal;
estimating a differential symbol timing from two consecutive bursts;
generating a detection metric;
comparing the obtained detection metric with predetermined threshold to determine the outage status.
In one aspect of the invention, a high altitude communication device generates a plurality of user link beams having a first communication characteristic and a feeder link having a first communication characteristic. A gateway terminal receives the user link beam. A user terminal has a receiver circuit for receiving a first received signal and a second received signal thereafter. The receiver circuit has a recursive filter for generating an amplitude estimate from said first received signal.
One advantage of the invention is that system detection accuracy may be increased by using further techniques such as dual threshold detection and multiple observation in addition to the basic amplitude determination.